1. Field of the Invention
This invention relates to a protective relay, more specifically, to a device and a method for processing an input data of a protective relay capable of restoring damage to allow a normal measurement if data stored in an accumulation buffer of the protective relay is damaged due to noise.
2. Description of the Related Art
In an electric power system, since various electric power plants are linked complicatedly, in case that a fault occurs at a position in the linked electric power system, the faulted section should be rapidly separated from the system, and a protective relay takes charge of such role.
With the rapid operation of the protective relay, one of important elements is an accurate operation. Accordingly, in case an ineffective value is measured due to external noises inputted to a DSP (Digital Signal Processor) for obtaining a standard value for determining operations of the protective relay, a erroneous operation may be generated if the ineffective value is processed without any correction there to. Therefore, there is a need to take a complementary measure.
Namely, a recovering method is necessary if the measurement value that is a standard for determining the protective relay is not effective. FIG. 1 is a flowchart showing a conventional processing procedure for analog input signal of the protective relay. As shown in the drawing, the analog signal inputted through detecting means such as power transformer (PT) and current convertor (CT) is transformed through an analog filter and an analog-digital converting part (ADC) into a digital data (S1˜S3).
Hereinafter, in the digital signal processing part (DSP), a phasor operation algorithm is prosecuted (S4). FIG. 2 is showing each of change of RMS values if analog input becomes 0. Herein, an AD_sample is a sampling data taken through the analog-digital converting part (ADC), an RMS is a value obtained by a RDFT (Recursive Discrete Fourier Transform) in the digital signal processing part (DSP).
FIG. 3 shows a case wherein ineffective signal is stored in an accumulation buffer of the RDFT due to external noise input at a point A of time.
In the case, as shown in the drawing, even though the analog input becomes 0, since the RMS value does not fall and keeps a constant value, it is not recovered before a rebooting is prosecuted.
This means that a erroneous operation may occur the moment a measurement value becomes larger than an operation preset value in relay elements controlling the operation based on size of the input signal. The erroneous operation should never occur in the protective relay.
Therefore, a complementary measure is essentially needed because the erroneous operation often occurs while displaying a constant measurement value even in a situation where there is no analog input in operation.